1. Field of the Invention
The subject invention relates to hydraulic power plants and components therefor, to hydraulic power units, to hydraulic drives, tools and other equipment, to reservoirs, to methods and apparatus for providing hydraulic powers, to methods and apparatus for circulating a liquid in a reservoir, and to heat exchange techniques.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent. Also, the following comments contain conclusions and observations which have only been drawn or become apparent after conception of the subject invention or which contrast the subject invention or its merits against the background of developments subsequent in time or priority.
Hydraulic power units typically include one or more reservoirs for the hydraulic fluid which is moved by one or more pumps driven by an internal combustion engine, an electric motor or other suitable drive.
Existing hydraulic power units typically include automobile-type wheels carrying a heavy frame structure on which the motor and pump assembly are mounted apart from a reservoir facility and required accessories.
Some existing hydraulic power plants and units have been equipped with heat exchange facilities, typically for cooling the circulating hydraulic fluid. Sometimes water required for cooling a hydraulically actuated tool has been used for this purpose. Existing heat exchangers in this respect have tended to remain within the confines of established heat exchanger technology.
Reference may in this respect be had to U.S. Pat. No. 222,889, by J. B. Gathright, issued Dec. 23, 1879 for a faucet equipped with a helix immersible into a coolant, U.S. Pat. No. 745,499, by G. R. Jarman, issued Dec. 1, 1903 for a heat interchanger employing a double helix, U.S. Pat. No. 949,216, by A. C. Canida, issued Feb. 15, 1910 for a coil protector for coolers employing a helical tube immersed in ice, U.S. Pat. No. 1,424,689, by C. W. Stone, for an air cooler with bifilar helix, U.S. Pat. No. 1,813,667, by H. L. Hartenstein, issued July 7, 1931, for an apparatus for cooling internal combustion engines having a helical coil exposed to cool air, U.S. Pat. No. 2,077,846, by R. M. McIlvana, issued Apr. 20, 1937 for a milk cooler employing a bifilar cooling coil, U.S. Pat. No. 2,292,692, by O. R. Huber, issued Aug. 11, 1942, for a liquid refrigerating unit including helical and serpentine cooling coils, U.S. Pat. No. 2,449,127, by H. W. Kleist, issued Sept. 14, 1948 for an apparatus for cooling the interior of containers, employing bifilar and serpentine cooling coils, U.S. Pat. No. 2,752,763, by O. J. Shepard, issued July 3, 1956 for a beverage cooling apparatus with finned cooling coils or tubing, and U.S. Pat. No. 3,556,199, by R. S. De Groote, issued Jan. 19, 1971 for free convection cooling method and apparatus with immersed radiator-type heat exchanger.
One problem with a transfer of such heat exchange technology to the hydraulic power source area is that it is possible for hot hydraulic fluid to flow through the reservoir without being subjected to the desired cooling effect by heat exchanger means located therein.
In a similar vein, existing hydraulic power units have a reservoir capacity which typically is significantly higher than the volume of the hydraulic fluid pumped per minute. By way of example, a rule of thumb in this respect is that the reservoir capacity should be up to two and one-half times as high as the volume pumped per minute. This in practice adds considerable bulk and weight to hydraulic power units and also requires the volume of stand-by oil or other hydraulic fluid to be rather high. Yet despite such high reserves, existing power units often are not able to effect a sufficient or optimum cooling of the circulating hydraulic fluid. This eventuates shut-downs or limits power capacity and unit performance.